Smith & Wesson M&P15 in 300 Whisper, 300 BLACKOUT

The Smith & Wesson M&P15 in 300 Whisper was an interesting rifle released in 2011. At a time when many manufacturers were embracing the 300 BLK cartridge, S&W went with the 300 Whisper.

As it turns out, it was a good choice, but one that doesn’t appear to have been financially successful.

Let’s jump into what the M&P 300 Whisper rifle was all about.

Introduction of the M&P15 300

In the fall of 2022, Smith & Wesson announced a new M&P15 rifle chambered in 300 Whisper. The rifle was offered in two basic configurations that were most obviously differentiated by the finish: matte black or Realtree APG camo.

SW 300 whisper

However, there were more differences than just finish.

The Realtree version of the M&P15 300 featured a 5/8-24 threaded barrel along with an A2-style flash hider, while the black version of the rifle used a Yankee Hill flash hider. Both rifles shipped with a 16″ barrel.

The black version of the 300 Whisper rifle had a free floating, 10″ quad rail for accessory attachments. Both rifles are “optic ready” with a Picatinny rail for the addition of traditional or electronic sights. No sights shipped with the gun from the factory.

What Is the 300 Whisper?

Smith & Wesson chambered these rifles in 300 Whisper. Compared to some other cartridges, this one is not well known by many shooters.

The 300 Whisper is a cartridge developed in the 1990s. Based on the .221 Fireball case, it is necked up to .30 caliber and designed to match the ballistics of 7.62×39 at supersonic velocities.

MP 15 300 blackout

One of the interesting things about this cartridge is that it can be loaded with heavy bullets to operate at subsonic speeds. When paired with a sound suppressor, the cartridge offers good knockdown power and a very modest sound signature.

It is said that the 300 BLK (aka .300 AAC BLACKOUT) cartridge was derived from the 300 Whisper. While I don’t believe this is precisely accurate, the fundamental truth is Smith & Wesson states that both cartridges will work equally well in this rifle.

Both the 300 Whisper and the 300 BLACKOUT cartridges are designed to work well with suppressors.

According to Smith & Wesson:

The feed ramps and gas system have been optimized to run effectively with a full-range of factory loaded sub-sonic and supersonic ammunition, both suppressed and unsuppressed. The barrel’s twist rate is compatible with a wide variety of bullet weights from 110 to 220+ grains.

Here’s a hands on look on the 300 Whisper rifles:

S&W M&P15 300 Whisper Specifications

Here are the specs on the 300 Whisper version of the M&P15 rifle:

Caliber.300 Whisper/300 BLK
Standard Magazine Capacity10 rounds
Barrel Length16″
Twist Rate1:7.5″
Overall Length32″-35″
Weight (unloaded)6.38 lbs
Receiver Material7075 T6 aluminum
Barrel Material4140 steel
FinishRealtree APG

What Happened to the S&W M&P15 300 Whisper?

Smith & Wesson no longer offers any rifle chambered for the 300 Whisper or 300 BLK cartridges. The first gun dropped from the catalog was the black “tactical” model.

Smith & Wesson kept the Realtree version of the M&P15 300 Whisper around longer than the black version. At some point, however, the company changed the official chambering from 300 Whisper to 300 BLK.

Here is the Smith & Wesson literature on the last 300 BLK/300 Whisper rifle offered by the company:

Updated: April 2, 2022

By Richard Johnson

Richard Johnson is a gun writer, amateur historian and - most importantly - a dad. He's done a lot of silly things in his life, but quitting police work to follow his passion of writing about guns was one of the smartest things he ever did. He founded this site and continues to manage its operation.